User`s guide

Chapter 4 ______________________________________________________________ Maintenance
VAISALA______________________________________________________________________ 133
chamber with built-in 10 dB sonic attenuators in each of the three sonic
paths. The margin verifier is shown in Figure 108 on page 134.
This test verifies the following:
- Transducer arm trueness, since the verifier can not be put into place
if an arm is bent
- Transmitter output power
- Transmitter and receiver transducer efficiency
- Receiver sensitivity
- Acoustic crosstalk from any transmitter to any receiver
- Electric crosstalk
- Automatic gain threshold detectors.
This test demonstrates that the sensor will work at high wind speeds
since the signal-to-noise ratio decreases as wind speed increases. As
wind speed increases, turbulence increases acoustic noise. At the same
time, acoustic lenses that form around the transducers (because of air
pressure gradients) reduce the received signal.
Since the margin verifier decreases the signal-to-noise ratio to a level
that is slightly lower than it would be with the highest allowed wind
speed by the sensor, a zero wind speed reading with the verifier in place
indicates accurate readings at high wind speeds.
The test consists of the following steps:
1. Slip the margin verifier over the three transducers (see Figure 108
on page 134).
2. In outdoor conditions, secure the zero wind flow by covering the
sensor and margin verifier.
3. The sensor must read less than 0.5 miles per hour (0.22 m/s) with
the margin verifier in place.